The aortic valve is one of four valves of the heart. De-oxygenated blood enters the right atrium via the vena cava. The heart contracts and pumps the blood through the tricuspid valve into the right ventricle. After another pump of the heart, the blood goes into the lungs to become oxygenated. Once oxygenated, the blood collects in the left atrium until the heart contracts again. This pushes it through the mitral valve into the left ventricle, until a pressure differential between the left ventricle and the aorta opens the aortic valve. The blood goes through the aortic valve to the aorta and on its way to deliver the oxygen to all the cells of the body.
Aortic stenosis, also called sub-aortic stenosis or aortic valve stenosis, is a disease in which the opening of the aortic valve is narrowed. This narrowing restricts the amount of blood flowing from the heart. This is the second-most common disease of the three main problems that make up “heart disease” in dogs. The seriousness depends upon how restricted the aortic valve becomes.
This disease may be caused by one of many factors. Most commonly, it results from a defect or malformation, or from an obstruction of some kind. Different things may cause these defects. Some cases of aortic stenosis are congenital, where the defects are present from birth. These congenital defects may be hereditary.
Some cases of aortic stenosis are caused by a bacterial infection of the left mitral valve and/or the aorta (endocarditis). The remaining cases are caused by age-related calcification. Any of these causes may be hastened by diabetes mellitus, uremia, or hypertension.
Although there is no solid evidence that sub-aortic stenosis is genetic, any animal that is the dam or sire of a dog diagnosed with congenital SAS should not be bred again. Definitely, any dog with this disease should be kept from the breeding pool. Sub-aortic stenosis caused by bacterial endocarditis can be prevented with the use of antibiotics after, during, and before medical procedures and dental cleanings.
This disease has many associated symptoms. Early stages of the disease may appear to be sub-clinical (without symptoms). As it progresses, a dog may display one or more of the following symptoms: weakness, difficulty breathing, fainting, rapid breathing, exercise intolerance, lethargy, heart murmur, dry cough, collapse, weak femoral pulse, irregular heartbeat, stunted growth, and sudden death. This sudden death usually occurs during or directly following a period of exertion or exercise. Some dogs may show no other signs of heart disease before this.
Dogs at Risk
Aortic stenosis is one of the most common congenital heart defects suffered by large and giant breeds, and is among the most common of congenital heart problems in all dogs. It is most commonly seen as a congenital defect suffered by Rottweilers, German Shepherd Dogs, Bull Terriers, Golden Retrievers, Boxers, Newfoundlands, Bouvier des Flandres, German Shorthaired Pointers, and Bernese Mountain Dogs. These dogs usually develop symptoms during the first few weeks or months of life.
Breeds prone to developing sub-aortic stenosis from non-congenital causes are Samoyeds, English Bulldogs, Great Danes, English Bulldogs, and Bull Terriers.
Testing and Diagnosis
Most cases of heart disease are found during a dog’s annual vet appointment – or at its first puppy check by a vet when he or she listens to the heart. If you suspect your dog has heart problems of any kind, get it to a vet immediately. The vet should take a detailed history and perform a physical exam. Urine and blood analysis should come back normal. Chest x-rays will often show an enlarged heart overall, or the left side will be noticeably larger than the right. ECG results may show a thickening of the left ventricular wall.
Advanced testing may include Doppler echocardiography to test the velocity and direction of blood flow through the heart’s chambers, contrast radiography (also called angiocardiography) to identify thickening of the heart’s walls and dilation of the aorta, and cardiac catheterization to compare the pressure across the dog’s AV valve to that a normal heart. Cardiac catheterization and contrast radiography are only rarely done due to the need to put the dog under general anaesthesia. Echocardiography is the best and safest way to diagnose SAS.
Treatment and Prognosis
There is no standard treatment protocol for subaortic stenosis. In the most severe cases, the main goals are to reduce the risk of syncope (fainting episodes) and sudden death. Cases where the heart disease has caused congestive heart failure, different medications to control that condition will be necessary. Dogs with SAS but no congestive heart failure may be prescribed reduced activity restriction, low-sodium diets, and should be removed from any breeding programs.
The only way to truly cure a dog with this condition is to perform open-heart bypass surgery. Sometimes a balloon is inserted using catheterization and is inflated to dilate the aorta.
Owners should talk to their vets about all the possible treatment options and decide what is best on a case-by-case basis.
Prognosis varies according to the severity of the dog’s disease. Dogs with mild cases may live a normal, long life, with few to no symptoms. Dogs with moderate to severe cases will often die suddenly within the first couple years of life, or develop congestive heart failure and die from that – or get euthanized.